1. Field of the Invention
The present invention relates to a safety electrical assembly for electric power equipment, more particularly for electric motor-driven lawn-mowers, hedge trimmers and other devices of the type supplied with at least three-wire power source.
2. Brief Description of the Prior Art
Known in the art, there is a Canadian patent no. 902,232 of E. Hundhausen et al., granted on Jun. 6, 1972. This patent describes a protective circuit for electrically driven lawn-mowers and the like including an auxiliary conductor so arranged in cross section of a cable, that before the main conductor insulation is cut the auxiliary conductor is severed and the current flowing through the auxiliary conductor is interrupted. Consequently, a relay, mounted in series with the auxiliary conductor, is deprived of current and its switches opened so that the whole cable connecting the equipment to an electrical power source is deprived of current.
Also known in the art, there is U.S. Pat. No. 3,659,152 of P. A. De Langis, granted on Apr. 25, 1972. This patent describes a ground detector and guard circuit which prevents operation of an appliance or instrument unless the associated source has a grounded conductor. This guard circuit includes a ground wire, a pair of line conductors, and a control relay having one terminal connected to the ground wire and respective neon lamps connected between the line conductors and another terminal of the control relay. If one of the line conductors is damaged or cut, the control relay is deprived of current and its switch opened, thereby preventing energization of an associated appliance or instrument. The absence of proper ground is signalled by the neon lamps.
Also known in the art, there is U.S. Pat. No. 3,426,342 of P. A. De Langis granted on Feb. 23, 1969. This patent describes another protective and guard circuit.
One drawback with the protective or safety circuits shown in the above patents is that they do not prevent operation of the electric equipment when the ground conductor of the cable connected between a housing of the equipment and the corresponding male plug is not operative.